7,308 research outputs found
Does innovation stimulate employment? A firm-level analysis using comparable micro data on four European countries
This paper studies the impact of process and product innovations introduced by firms
on their employment growth. A model that relates employment growth to process innovations
and to the growth of sales due to innovative and unchanged products is derived and
estimated using a unique source of comparable firm-level data from France, Germany,
Spain and the UK. Results for manufacturing show that, although process innovation
tends to displace employment, compensation effects are prevalent, and product innovation
is associated with employment growth. In the service sector there is less evidence of
displacement effects, and growth in sales of new products accounts for a non-negligible
proportion of employment growth. Overall the results are similar across countries, with
some interesting exceptions
The Effects of Variations in Nuclear Interactions on Nucleosynthesis in Thermonuclear Supernovae
The impact of nuclear physics uncertainties on nucleosynthesis in
thermonuclear supernovae has not been fully explored using comprehensive and
systematic studies with multiple models. To better constrain predictions of
yields from these phenomena, we have performed a sensitivity study by
post-processing thermodynamic histories from two different hydrodynamic,
Chandrasekhar-mass explosion models. We have individually varied all input
reaction and, for the first time, weak interaction rates by a factor of ten and
compared the yields in each case to yields using standard rates. Of the 2305
nuclear reactions in our network, we find that the rates of only 53 reactions
affect the yield of any species with an abundance of at least 10^-8 M_sun by at
least a factor of two, in either model. The rates of the 12C(a,g), 12C+12C,
20Ne(a,p), 20Ne(a,g) and 30Si(p,g) reactions are among those that modify the
most yields when varied by a factor of ten. From the individual variation of
658 weak interaction rates in our network by a factor of ten, only the stellar
28Si(b+)28Al, 32S(b+)32P and 36Ar(b+)36Cl rates significantly affect the yields
of species in a model. Additional tests reveal that reaction rate changes over
temperatures T > 1.5 GK have the greatest impact, and that ratios of
radionuclides that may be used as explosion diagnostics change by a factor of
less than two from the variation of individual rates by a factor of 10.
Nucleosynthesis in the two adopted models is relatively robust to variations in
individual nuclear reaction and weak interaction rates. Laboratory measurements
of a limited number of reactions would help to further constrain predictions.
As well, we confirm the need for a consistent treatment for relevant stellar
weak interaction rates since simultaneous variation of these rates (as opposed
to individual variation) has a significant effect on yields in our models.Comment: accepted by A&A, 14 pages, 5 figures, 2 table
Anomalous spin-charge separation in a driven Hubbard system
Spin-charge separation (SCS) is a striking manifestation of strong
correlations in low-dimensional quantum systems, whereby a fermion splits into
separate spin and charge excitations that travel at different speeds. Here, we
demonstrate that periodic driving enables control over SCS in a Hubbard system
near half-filling. In one dimension, we predict analytically an exotic regime
where charge travels slower than spin and can even become 'frozen', in
agreement with numerical calculations. In two dimensions, the driving slows
both charge and spin, and leads to complex interferences between
single-particle and pair-hopping processes.Comment: arXiv admin note: text overlap with arXiv:2002.0231
Perturbation of the sierpinski antenna to allocate the operating bands
A scheme for modifying the spacing between the bands of the Sierpinski antenna is introduced. Experimental results of two novel designs of fractal antennas suggest that the fractal structure can be perturbed to enable the log-period to be changed while still maintaining the multiband behaviour of the antenna.Peer ReviewedPostprint (published version
Spatial and temporal stability of weed patches in cereal fields under direct drilling and harrow tillage
The adoption of conservation agriculture (CA) techniques by farmers is changing the dynamics of weed communities in cereal fields and so potentially their spatial distribution. These changes can challenge the use of site-specific weed control, which is based on the accurate location of weed patches for spraying. We studied the effect of two types of CA (direct drilling and harrow-tilled to 20 cm) on weed patches in a three-year survey in four direct-drilled and three harrow-tilled commercial fields in Catalonia (North-eastern Spain). The area of the ground covered by weeds (hereafter called “weed cover”) was estimated at 96 to 122 points measured in each year in each field, in 50 cm × 50 cm quadrats placed in a 10 m × 10 m grid in spring. Bromus diandrus, Lolium rigidum, and Papaver rhoeas were the main weed species. The weed cover and degree of aggregation for all species varied both between and within fields, regardless of the kind of tillage. Under both forms of soil management all three were aggregated in elongated patterns in the direction of traffic. Bromus was generally more aggregated than Lolium, and both were more aggregated than Papaver. Patches were stable over time for only two harrow-tilled fields with Lolium and one direct-drilled field with Bromus, but not in the other fields. Spatial stability of the weeds was more pronounced in the direction of traffic. Herbicide applications, crop rotation, and traffic seem to affect weed populations strongly within fields, regardless of the soil management. We conclude that site-specific herbicides can be applied to control these species because they are aggregated, although the patches would have to be identified afresh in each season.This research was funded by the Spanish National Program (project: AGL2010-22084-C02-0). A.E.M. was funded by the Institute Strategic Programme (ISP) grants, “Soils to Nutrition” (S2N) grant number BBS/E/C/000I0330, and the joint Natural Environment Research Council (NERC) and Biotechnology and Biological Sciences Research Council (BBSRC) ISP grant “Achieving Sustainable Agricultural Systems” (ASSIST) grant number BBS/E/C/000I0100, using facilities funded by the BBSRC
Adiabatic Splitting, Transport, and Self-Trapping of a Bose-Einstein Condensate in a Double-Well Potential
We show that the adiabatic dynamics of a Bose-Einstein condensate (BEC) in a
double well potential can be described in terms of a dark variable resulting
from the combination of the population imbalance and the spatial atomic
coherence between the two wells. By means of this dark variable, we extend, to
the non-linear matter wave case, the recent proposal by Vitanov and Shore
[Phys. Rev. A 73, 053402 (2006)] on adiabatic passage techniques to coherently
control the population of two internal levels of an atom/molecule. We
investigate the conditions to adiabatically split or transport a BEC as well as
to prepare an adiabatic self trapping state by the optimal delayed temporal
variation of the tunneling rate via either the energy bias between the two
wells or the BEC non-linearity. The emergence of non-linear eigenstates and
unstable stationary solutions of the system as well as their role in the
breaking down of the adiabatic dynamics is investigated in detail.Comment: 8 pages, 7 figure
STELLAR ORIGINS OF EXTREMELY C-13- AND N-15-ENRICHED PRESOLAR SIC GRAINS: NOVAE OR SUPERNOVAE?
Extreme excesses of 13C (12C/13C < 10) and 15N (14N/15N < 20) in rare presolar SiC grains have been considered diagnostic of an origin in classical novae, though an origin in core collapse supernovae (CCSNe) has also been proposed. We report C, N, and Si isotope data for 14 submicron- to micron-sized 13C- and 15N-enriched presolar SiC grains (12C/13C < 16 and 14N/15N < ~100) from Murchison, and their correlated Mg–Al, S, and Ca–Ti isotope data when available. These grains are enriched in 13C and 15N, but with quite diverse Si isotopic signatures. Four grains with 29,30Si excesses similar to those of type C SiC grains likely came from CCSNe, which experienced explosive H burning occurred during explosions. The independent coexistence of proton- and neutron-capture isotopic signatures in these grains strongly supports heterogeneous H ingestion into the He shell in pre-supernovae. Two of the seven putative nova grains with 30Si excesses and 29Si depletions show lower-than-solar 34S/32S ratios that cannot be explained by classical nova nucleosynthetic models. We discuss these signatures within the CCSN scenario. For the remaining five putative nova grains, both nova and supernova origins are viable because explosive H burning in the two stellar sites could result in quite similar proton-capture isotopic signatures. Three of the grains are sub-type AB grains that are also 13C enriched, but have a range of higher 14N/15N. We found that 15N-enriched AB grains (~50 < 14N/15N < ~100) have distinctive isotopic signatures compared to putative nova grains, such as higher 14N/15N, lower 26Al/27Al, and lack of 30Si excess, indicating weaker proton-capture nucleosynthetic environments
Exact and heuristic allocation of multi-kernel applications to multi-FPGA platforms
FPGA-based accelerators demonstrated high energy efficiency compared to GPUs and CPUs. However, single FPGA designs may not achieve sufficient task parallelism. In this work, we optimize the mapping of high-performance multi-kernel applications, like Convolutional Neural Networks, to multi-FPGA platforms. First, we formulate the system level optimization problem, choosing within a huge design space the parallelism and number of compute units for each kernel in the pipeline. Then we solve it using a combination of Geometric Programming, producing the optimum performance solution given resource and DRAM bandwidth constraints, and a heuristic allocator of the compute units on the FPGA cluster.Peer ReviewedPostprint (author's final draft
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